Furfural and related compounds are useful precursors and starting materials for industrial chemicals for use as pharmaceuticals, herbicides, stabilizers, and polymers. Furfural is commonly made by dehydration of xylose or hemicellulose under acidic conditions. The current furfural manufacturing process utilizes biomass such as corn cob, switchgrass or wood waste as a raw material feed stock for obtaining xylose or hemicellulose, while very little value is obtained for the other major components such as cellulose and lignin except for energy production. With the evolution of ethanol industry, the availability such biomass material is expected to become limited. The objective of this invention is to render complete utilization of biomass, where the cellulose and a major portion of hemicellulose still can be directed toward biofuel production via enzymatic saccharification and fermentation followed by utilization of non-fermentable sugars in the waste stream for furfural production.
The production of ethanol from biomass, via enzymatic saccharification and fermentation of a major portion of hemicellulose and cellulose, results in the concurrent production of a waste stream known as “whole stillage” from distillation in the range of up to 20 liters of stillage per liter of ethanol. The carbohydrates in whole stillage comprise some non-fermentable branched pentose sugars in their oligomeric forms. Following solid/liquid separation of the whole stillage “thin stillage” is obtained. Thin stillage can be evaporated to produce the “syrup” which is burned to extract caloric values from it. Hereafter, whole stillage and thin stillage are referred to as “stillage”.
An alternative means to using some of the non-fermentable sugars locked in the stillage or syrup, to minimize carbon waste and reduce the negative environmental impact resulting from burning of the syrup, is to develop methods to extract useful chemicals from it. For example, furan derivatives, such as hydroxymethylfuran (HMF) and furfural, which can serve as platforms for different chemicals and fuel productions, can be produced from agricultural waste material (Amiri, H. et al., Carbohydrate Research, 345(15), (2010) 2133-2138).
Conventionally, furfural can be produced from pentose sugars obtained from hydrolysis of the hemicellulose contained in biomass. Typically, hydrolysis of biomass is performed with aqueous acids at relatively high temperatures to obtain C5 and C6 sugars derived from xylan and glucan, respectively. Any furfural generated in this process, when left in the monophasic aqueous reaction mixture of sugars, can undergo degradation via condensation initiated by reactive sugar intermediates, resulting in lower yield of the desired furfural product. Furthermore, costly separation steps are then required to isolate the furfural from other intermediates, thus increasing complexity of the process.
U.S. Patent Application Publication No. 2008/0033188 relates to a process to make furan derivative compounds. The process comprises dehydrating a carbohydrate feedstock solution, optionally in the presence of an acid catalyst, in a reaction vessel containing a biphasic reaction medium comprising an aqueous reaction solution and a substantially immiscible organic extraction solution. The aqueous reaction solution, the organic extraction solution, or both the aqueous reaction solution and the organic extraction solution, contain at least one modifier to improve selectivity of the process to yield furan derivative compounds in general, and HMF in particular.
Current methods do not describe complete utilization of all the valuable carbohydrates in the biomass. In particular, methods for producing useful chemicals from non-fermentable branched sugars in stillage or syrup are therefore highly desirable.